This invention relates to an acceleration slip controller for controlling a slip that occurs between the driving wheel and the road surface during vehicle acceleration.
When an acceleration slip occurs, the vehicle does not accelerate as desired and fuel is wasted. For preventing the acceleration slip, various inventions have been disclosed. One of the inventions is disclosed by the assignee of the present application in the Japanese Unexamined Published Patent Application No. 61-85248 in which the acceleration slip on the driving wheel (or excessive revolution of the driving wheel during vehicle acceleration) is quickly reduced with the use of the engine output control and with the use of the braking system of the driving wheel. Among the measures to slow the driving wheels'revolution, a powerful braking system is utilized which causes mechanical wear of the brake pad and other parts. Therefore, another invention is disclosed in the Japanese Patent Application No. 60-294439 in which the engine output control is preferably executed rather than the brake control when the slip rate of the driving wheel is small, and the the brake control is started when the slip rate increases.
When both the engine output control and the brake control are prepared for reducing the acceleration slip, the initiation of each control is deliberately controlled. However in the prior art, when both controls are executed during a large slip rate condition, the engine output control and the brake control are executed independently. At this time, each of the control systems performs feedback control for adjusting the actual slip rate of the driving wheel toward a target slip rate (or to a target revolution speed). But, since the target is the same between the two control systems, the two controls are somewhat correlated rather than completely independent. As described above, the braking force is so strong in reducing the revolution speed of the driving wheel that the responsiveness of the brake feedback system is ten times faster than that of the engine output control system. When both the controls are executed without adjustment of the imblance in responsiveness, the engine output control is largely influenced by the brake control. Consequently, when the brake control is initiated during the engine output control, the engine output starts fluctuating greatly. This leads to vibration of the vehicle body and to a deteriorated control of the acceleration slip in which the feedback hunting persists and the acceleration is not efficiently controlled.